- Fire zone – what area should it include?
- Should E30-90 cable routes in accordance with DIN be provided in class E buildings?
- What is the difference between a potentially explosive zone and a potentially explosive room?
- In the potentially explosion hazard zone, do all components must be EX?
Fire zone – what area should it include?
According to most of the standards and guidelines, as a fire zone we assume a closed space surrounded by barriers with fire resistance, which ensures that the fire does not spread from this space and to that space at a given time.
Accordingly, the fire zone can be called either:
- the entire building, if there are no fire-resistant barriers inside,
- the entire floor, which is closed with ceilings with fire resistance (the same condition applies to the walls of the staircase),
- one room, if it is closed with partitions / walls with fire resistance.
What to do, e.g. with a hotel where all rooms may be legally closed with fire barriers, or with a typical electrical or technological building, where similar rooms are also closed with fire resistance partitions.
Additionally, it should be noted that the fire zone is the basis for:
- the adoption of the legal requirements for buildings and their parts,
- development of evacuation conditions,
- adopting work algorithms for fire automation and alarm systems,
- designing fire extinguishing installations or placing internal hydrants.
Taking into account the above input data, the division into zones should correspond to:
- The essence of threats in individual spaces,
- The functional needs of building users, as a significant disturbance of this may result in a reduction of the building’s efficiency / profitability and the purpose of the building for which it was built,
- Architectural and construction solutions.
It should be added that, in accordance with part of the guidelines, as well as everyday practice, it is possible to divide buildings into fire zones, which contain rooms individually separated by fire, but they are included in a given fire zone, where, for example, there are rooms that should be protected against fire development from and to them, while they are functionally related to other rooms in a given fire zone, e.g .:
- control room – protection of operating personnel,
- electric traffic rooms – supplying important circuits in the building, and also significant fire hazards for the building,
- archives or server rooms – essential for the company’s operation.
Should E30-90 cable routes in accordance with DIN be provided in class E buildings?
Contrary to the myths circulating around the country, the answer is: there is no such requirement or need.
In buildings belonging to the fire resistance class E, no requirements are imposed on the building structure. These are buildings either well protected by automatic water fire extinguishing systems or without significant fire hazards.
If there are no fire resistance requirements for the primary structure, why should we require this for the secondary structure attached to the first? The answer is: no one knows why.
Some people say that according to the technical documents for cables classified as PH30-90, they should only be attached / laid on routes E30-90. Here, I always refer to the requirements for routes E30-90, where there is also a provision saying that these ladders or shelves must be attached to the ground with R30-90 fire resistance. And how to do it in a building with fire resistance class E? You can’t because there is no such need.
To sum up, the use of cable routes in execution E in accordance with the DIN standard in buildings with fire resistance class E is not justified, and also required, even if we lay PH cables on them.
It should be noted that cables in such buildings often have PH30-90 when they supply circuits that must be operated during a fire, e.g. emergency lighting or smoke flaps, because they are usually supplied from other fire zones, and due to the lack of possibility of splitting them along their entire length they are classified as PH30-90.
Finally, Polish law does not require the use of E30-90 cable routes, while the Regulation of the Minister of Infrastructure Technical Conditions … states that a properly selected cable assembly should be provided, which under given conditions will guarantee the transfer of electrical power or signals during a fire. When you ask what special requirements should be provided for cable routes / cable assemblies in a building that is free from significant fire hazards or well protected by fixed water fire extinguishing systems, the answer is: no special requirements are justified under such conditions as there is no risk of thermal impact which can damage the cable assembly in the required time.
What is the difference between a potentially explosive zone and a potentially explosive room?
The terminology, quite similar, causes frequent confusion of these concepts.
An explosion hazard zone is a space in which there is an explosive atmosphere, i.e. a concentration of flammable dust / gases (vapors) in a concentration between the lower and upper explosive limits (mixed with air).
Additionally, we have a specific Polish supplement included in the Regulation of the Ministry of Interior and Administration on Fire Protection of Buildings (Journal of Laws No. 109, item 719 of 2010), defining the minimum volume of an explosive atmosphere at 0.01 m3, for which the explosion hazard zone is classified. Hardly anyone is counting it, but in this way the classification of zones with very low emissions can be excluded.
The explosion hazard zone may have a local range (also indoors) or fill the entire room.
An explosive room is a strictly legal expression (occurring mainly in Polish legislation), which defines a room in which a potential explosion (with a classified zone) will result in a pressure increase greater than 5kPa. Someone has proposed this pressure, which is assumed to be the minimum capable of overturning an adult human.
In connection with the above, there may be an explosion hazard zone that does not result in the classification of the room as potentially explosive (this applies primarily to large cubature rooms or zones with low flammable emissions), while a room with an explosion hazard must always be associated with the classification of the explosion hazard zone and most often they are rooms with small cubatures.
It should be added that the consequences of classifying a room as potentially explosive are very serious, because, among others:
- these rooms may only be located directly under the roof (they cannot be located on the lower floors in multi-storey buildings),
- it is required to provide an appropriate relieving surface or a “light” roof structure within the meaning of the Regulation of the Minister of Infrastructure on technical conditions … (Journal of Laws of 2019, item 1065),
- the building containing such a room should be at least 20 m away from other buildings,
- internal walls of this room should be resistant to pressure greater than 15 kPa …
These are very strict requirements, even for relatively small explosions, which at 6-15 kPa will not have such a high impact force, but replacement conditions (exceptions) for similar rooms are not accepted, so in some cases it is necessary to enter into the technology strongly, to avoid a similar classification of the room, because in some buildings it limits the possibility of the planned operation.
In the potentially explosion hazard zone, do all components must be EX?
The answer is: yes and no.
The most important criterion for further analysis is the value of the minimum ignition energy of the combustible material that creates an explosive atmosphere.
The minimum ignition energy is the amount of energy measured in mJ that is capable of igniting a given explosive atmosphere.
Therefore, if a given energy source is greater than the minimum ignition energy, then such an emitter (component) should be provided in an explosion-proof EX version and meet the criteria for a given explosive atmosphere (type of focus, device category, temperature class, explosion group), on the other hand, if the energy source does not exceed the value of the minimum ignition energy, such a component may be in a “normal” design.
To sum up, there are substances with a very low minimum ignition energy, e.g. hydrogen or methane (below 1 mJ), for which all components must have EX execution in accordance with the ATEX Directive, while in the case of substances with a high minimum ignition energy, e.g. ammonia (more than 500 mJ) or PVC or coal dust (hard or brown), the minimum ignition energy of which exceeds 1000 mJ, it is worth analyzing which components can actually be energy emitters with a value greater than the minimum ignition energy, because e.g. atmospheres with PVC or soot can only be set on fire with an open flame.
The above analysis should be subject to the risk assessment included in the Explosion Hazard Document.